Sample on http://silverlight.services.live.com/invoke/6655/NavSplash/iframe.html
Discussion http://forums.silverlight.net/forums/p/134965/301270.aspx

This is a royal theme for windows xp

This theme provides a consitent look for navigation templates and all Controls found in the control toolkit.
This is a SL3 Theme Project.
You find the Theme DLL in the ClientBin folder.

Silverlight 3 navigation theme

This is the "Retro" theme for the Silverlight Business Application project template provided by .NET RIA Services installation. Extract the contents of this download and place the Styles.xaml in the projects Asset folder.

This is the "Skyline" theme for the Silverlight Business Application project template provided by .NET RIA Services installation. Extract the contents of this download and place the Styles.xaml in the projects Asset folder.

This is the "Subdued" theme for the Silverlight Business Application project template provided by .NET RIA Services installation. Extract the contents of this download and place the Styles.xaml in the projects Asset folder.

This is the "Mediterranean Sun" theme for the Silverlight Business Application project template provided by Visual Studio Tools for Silverlight and .NET RIA Services. Extract the contents of this download and place the Styles.xaml in the projects Asset folder.

This is the "Seeing Sound" theme for the Silverlight Business Application project template provided by Visual Studio Tools for Silverlight and .NET RIA Services. Extract the contents of this download and place the Styles.xaml in the projects Asset folder.

This is the "Seeing Sound" theme for the Silverlight Navigation Application project template provided by Visual Studio Tools for Silverlight. Extract the contents of this download and place the Styles.xaml in the projects Asset folder.